Oilfield chemical applications require robust surfactants that can provide good foaming at elevated temperatures and/or pressures. Suitable surfactants for this purpose include long-chain (C16-C18 or C20-C24) alpha-olefin sulfonates, alkyl aryl sulfonates, and salts of alpha-olefin sulfonic dimer acid (“AOS dimer acid,” see, e.g., U.S. Pat. Nos. 4,556,107; 4,567,232; 4,607,700; 4,957,646; and U.S. Pat. No. 5,052,487). Dilute blends of alpha-olefin sulfonates and unsaturated fatty acids (e.g., oleic acid) have been used as steam foaming agents (see, e.g., U.S. Pat. No. 5,279,367).
Dimerization of alpha-olefin sulfonic acid (“AOS acid”) is described, for example, in U.S. Pat. Nos. 3,721,707 and 3,951,823. Briefly, AOS acid produced by sulfonation of one or more alpha-olefins, is heated at 110° C. to 200° C. to induce oligomerization. Under these conditions, intermediate sultones and alkenesulfonic acids are converted to alkanesulfonic acids and other products. The molecular weight of the product is roughly double that of the AOS acid, and hence the term “AOS dimer acid” to describe it. However, the structure of the product can be rather complex, as illustrated in the '707 patent.
AOS dimer acid salts and other known alternative foamers were designed for use at temperatures commonly used for steam flooding, typically 160° C. to 180° C., while other oil recovery processes require foamers that can withstand even higher temperatures and pressures. One such process is steam-assisted gravity drainage (“SAGD”), which uses gravity to cause bitumen present in tar sands or other heavy oil deposits to melt and flow to a production well (see, e.g., U.S. Pat. No. 4,344,485 and Can. Pat. No. 1,304,287). SAGD applications may benefit from foamers that can perform well and resist thermal degradation at temperatures in the 210° C. to 250° C. range. So far, there are few suitable options, although AOS dimer acid salts are among the best known foamers for this purpose.
The oilfield chemicals industry would benefit from the availability of surfactants that can provide good foaming performance and thermal stability at the high temperatures and pressures utilized in SAGD and other oil recovery processes. Ideally, the surfactants would be straightforward to produce using conventional equipment and techniques and would provide improved high-temperature performance when compared with AOS dimer acid salts.